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Lecture 10

BIOL 1030 Lecture 10: Lecture 10
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Department
Biological Sciences
Course
BIOL 1030
Professor
Scott Kevin
Semester
Winter

Description
Lecture 10 o The four basic stages of food processing include: ingestion, digestion, absorption, elimination. o Ingestion is basically feeding – how animals bring food into their digestive tract. There are four basic ways in which this is performed. o One way in which this occurs in with suspension feeding (also known as filter feeding) in which animals filter particles suspended in the water column – only in aquatic animals (little floating in the air). o For example, a baleen whale has modified their teeth into baleen (which are comb-like structures) that takes a big gulp of sea water and forces the water out after filtering out the krill in the water. o Sponges also filter feed as water is bathed through their bodies and as it goes through the choanoderms, the collars of the cell trap suspended particles (debris, microbes in the water, etc.). Basically, filter the water for the food they need. o Another form of ingestion is substrate feeding (leaf-minor insect larvae living within the mesophyll layer of the leaf). o The leaf – substrate – is its habitat/environment, as it moves through the mesophyll it eats it and receives the nutrients. o Therefore, a substrate feeder feeds off of its environment. Another example are earthworms (they eat the soil they crawl through). o Fluid feeding also occurs in which animals live almost entirely off of a fluid diet. Aphids bite into a green plant and suck out the fluid (want the sugar built through photosynthesis). o Aphids need to eat a lot of the photosynthates to receive enough nutrients in their diet to sustain them, however, their waste usually has a lot of sugar – honeydew – which is consumed by ants. o Another example of a fluid feeder is mosquitoes that feed on blood (many organisms do such as well). o The most common feeding mechanism for ingestion in the animal kingdom is bulk feeding. This involves a predator feeding on a prey (whole or in pieces). o In order for an animal to feed by this mechanism they need to ingest the animal either whole (daphnia ingested by a hydra – with a modified jaw (anaconda) which can dislocate on demand) or in pieces. o For ingestion of chunks of prey to occur the organism needs to have modified teeth to cut the prey into large pieces (eating animals in chunks and with pieces torn off is the more derived characteristic – more evolutionarily advantageous to do so). o The reason why it is evolutionarily advantageous is because a certain prey has a specific volume with a set number of calories that can be used as fuel. o An animal’s enzymes that work on the prey they swallowed can only work on the surface of the animal. o Therefore, physically breaking down the preyinto pieces increases the surface area for the samevolumethat the animal’s enzymes canprocess andso morecalories canbeobtained. o Therefore, bulk feeding of pieces of the prey is a much more efficient and advantageous feeding mechanism. o It does, however, require adaptation of certain structures to get the whole prey into pieces (teeth, claws, etc.). o Mammalian teeth have adaptations depending on the diet they consume. o The mammalian mouth consists of four main types of teeth: • Incisors – at the front of the mouth. Tearing small pieces off, nipping small flesh or plant material • Canines – fangs, sharp and pointy. Used as a weapon to take down prey • Premolars – cutting type. Fit together like scissors – “shearing teeth” very good for cutting meat • Molars – grinding. Flat surface – come together for effective grinding. o Each type of teeth has a different structure and so a different function. o Humans are omnivore (evolved to consume both plant and animal material), we have the teeth to deal with this adaptation. o Herbivores (animals eatingsolelyplantmaterial),themost important ofthefourteeth types are the grinding molars which are needed to break down the cell wall material to get to the nutritious material in the plant cell. o Therefore, they have large and pronounced molars. At the front, they also have developed incisors which maybe useful for cutting grass from the ground or leaves from the branches of trees. o Canines aren’t generally required in herbivores, so they are generally reduced (small or not present). Premolars are also reduced, as they don’t consume flesh to cut and shear. o Carnivores (animals feeding entirely on other animals – meat) have a different dental formula. They have very large canines to help the animal in capturing and killing their prey. o They also have very pronounced premolars (serrated) as they are very sharp and fit together nicely for the animal to easily tear chunks of meat off of their prey. o They have very few or no molars as they generally don’t get used (as most carnivores simplytear off a chunk of flesh and swallow it – theydo not spend much time chewing and grinding their food). o Chewing is the first stage of digestion (mechanical digestion) where large objects are broken down, torn or grinded into smaller pieces (the molecular structures of the food is not altered). o Chemical digestion involves the breaking of bonds between atoms in the molecules that is consumed. Chemical digestion can occur within the cell (in vesicles – intracellular digestion). o Sponges rely entirely on intracellular digestion within the choanocytes. Food particles in the water are filtered and enter the cell through vesicles where they are broken down. o All other animals have some quantity of intracellular digestion (humans break down tripeptides within cells). Every other organism in the animal kingdom also has extracellular digestion. o For example, the daphnia is digested in the gastrovascular cavity (chamber) of the hydra. This occurs via enzymes that are dumped into the gastrovascular cavity, which break down the macromolecules of the food into monomers that are absorbed by the cells. Still some intracellular digestion occurs.
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